1. Field of the Invention
The invention generally relates to switched reluctance motors and, in particular, a sensorless switched reluctance motor and its method of manufacture.
2. Description of the Prior Art
Dynamoelectric machines such as switched reluctance motors comprise a rotor assembly and a stator assembly with respect to which the rotor assembly is movable. The machine may be a polyphase machine having 2, 3, 4, or 5 phases, for example. For such machines, the stator assembly includes a plurality of phase windings which are energized in a particular sequence depending upon the type of machine usage. The stator assembly includes a plurality of inwardly salient teeth spaced about the inner circumference of the stator assembly. The rotor includes a plurality of outwardly salient rotor teeth. Inherent in the construction of the motor are a wide variety of features. For example, the number of rotor teeth may equal the number of stator teeth. Also, the width of the respective rotor and stator teeth may differ. There is also usually a defined air gap between the rotor teeth and the stator teeth. This gap should be uniform about the perimeter of the stator and rotor assemblies. However, in actuality, there are usually variations in the air gap which can be discerned when the rotor teeth sweep past the stator teeth during machine operation. Stator windings are to befitted so they span a stator tooth. This may be arranged so portions of adjacent windings are side-by-side in a stator slot. Or, a winding may be arranged one above the other.
Sensorless switched reluctance motors and their methods of operation and manufacture generally depend on stored information of the flux-current-rotor position characteristics of the motor. The storage of this information entails a two-dimensional array to achieve acceptable accuracy. Some methods are only appropriate for relatively low speed operation for which the well known xe2x80x98choppingxe2x80x99 mode of current control applies and other methods are only appropriate for relatively high speed operation for which the well known xe2x80x98single-pulsexe2x80x99 mode of current control applies. While generally effective, it has been found that in some instances, the commutation angle control analysis is effected by bus ripple, transients on the bus, variations in the inductance characteristics from motor to motor and similar phenomena.
The physical structure of a motor which results from the above, in addition to the size and shape of machine stator and rotor laminations, creates an inherent electromagnetic environment within the motor. When the windings are side-by-side in a stator slot, it is desirable that the cross sectional pattern of the windings be substantially the same from motor to motor to minimize variations in the inductance characteristics from motor to motor. There is a need for a switched reluctance motor and its method of manufacture which will consistently produce motors which have small variations in their inductance characteristics from motor to motor.
The motor and method of the invention has a number of advantages over the prior art. The method results in a switched reluctance motor having windings that form a consistent cross sectional pattern from motor to motor so that the motors have similar and consistent inductance characteristics. Stators of such motors do not have significant inductance variations from stator to stator so that such stators may be used as part of sensorless switched reluctance motors. The method separates the windings as the windings are inserted in the stator slots so that a repeatable pattern within each slot is created.
In one form the invention comprises a method of manufacturing a switched reluctance motor comprising the steps of:
providing a stator core having slots for receiving windings and having an opening for receiving a rotor for rotational about a rotational axis;
positioning a separator adjacent to the stator to define to two separate sections in each of the slots, the sections having a contiguous side defined by a radial line passing through the rotational axis;
guiding wire by the separator into the slots to form the windings in the slots such that each slot has two different windings therein, one winding in each of the separate sections of each slot, and such that one of the windings in a particular slot is separated substantially along the radial line from the other winding in the particular slot; and
inserting a rotor in the opening of the stator; and
completing the assembly of the motor.
In another form, the invention comprises a method of manufacturing a switched reluctance motor comprising the steps of:
providing a stator having N teeth with N slots therebetween for receiving first, second and third windings and having an opening for receiving a rotor for rotational about a rotational axis;
providing N guides having N gaps therebetween wherein the N guides correspond to the N teeth and the N gaps correspond to the N slots;
positioning the windings in the N gaps;
positioning a separator such that each gap is separated into two sections substantially along a radial line passing through the rotational axis;
positioning the stator on the N guides such that the slots correspond to the gaps and each slot has two separate sections which correspond to the two separate gap sections;
guiding the positioned windings by the separator into the slots of the stator such that each slot has two different windings therein, one winding in each of the two separate sections of each slot, and such that one of the windings in a particular slot is separated substantially along the radial line from the other winding in the particular slot; and
completing the assembly of the motor.
In another form, the invention is switched reluctance motor comprising a stator core having slots and a plurality of windings positioned within the slots such that each slot has two windings therein. One of the windings in a particular slot is separated substantially along a radial line from the other winding in the particular slot. A rotor is received within the core.
Other objects and features will be in part apparent and in part pointed out hereinafter.